The present invention relates generally to clutches, and more specifically to radial clutches. Most specifically, the present invention relates to radial, bi-directional, one-way clutches used in on-demand four-wheel-drive vehicles.
On-demand four wheel drive systems are known in the art. Examples of on-demand four wheel drive systems include electronically-controlled systems and mechanically-controlled systems. Electronically-controlled systems have a disadvantage in that they are expensive to manufacture and repair. Mechanically-controlled systems have historically been complicated and complex. Accordingly, there is a need for a simple and inexpensive bi-directional, one-way clutch that is mechanically-controlled. Accordingly, the present invention is hereby presented.
Four-wheel drive motor vehicles are becoming increasingly popular. Recently, certain motor vehicles have been provided with xe2x80x9cfull-timexe2x80x9d four-wheel drive systems also known as all-wheel drive systems. In such all-wheel drive systems, the torque transfer cases are typically provided with an interaxle differential for dividing torque between the front and rear wheels of the motor vehicle. The interaxle differential enables the front wheels and the rear wheels to rotate at different speeds, during normal turning of the motor vehicle or in the event that the front wheels and the rear wheels have tires with different diameters. However, to prevent excessive relative slipping between the front wheels and the rear wheels, as might occur when one set of wheels encounters a low-traction condition, such as ice, these transfer cases typically include a selectively engageable clutch which is operative to lock the interaxle differential upon sensing a predetermined amount of relative slippage between the front output shaft and the rear output shaft of the transfer case. Locking of the interaxle differential prevents any further relative overrun or differentiation between the front output shaft and the rear output shaft of the transfer case.
Known prior all-wheel drive systems have generally required complex electronic sensors or other complex systems to monitor the overrun or differentiation between the transfer case front and rear output shafts or the front wheels and the rear wheels of a motor vehicle. Upon sensing relative overrun or differentiation, an electronic control system determines whether the relative overrun or differentiation being encountered is within a xe2x80x9cnormalxe2x80x9d expected range or is xe2x80x9cexcessive.xe2x80x9d If the electronic control system indicates that the overrun or differentiation is xe2x80x9cexcessive,xe2x80x9d the electronic control system causes the clutch to lock the interaxle differential to preclude any further relative overrun or differentiation. An electronic control system of this type can be expensive to manufacture and maintain and a more cost-effective, simplified xe2x80x9con demandxe2x80x9d system of limiting more than a predetermined amount of overrun or differentiation between the front wheels and the rear wheels of the motor vehicle would be desirable.
In recent years, motor vehicle all-wheel drive power-train systems have been cost-reduced by eliminating the transfer case differential, providing continuous power to a primary axle, and providing on-demand power to the secondary axle whenever primary axle slippage occurs. Typically, a torque-coupling device (viscous, hydraulic, electric) is utilized within the transfer case to drive the secondary axle. The torque-coupling device compensates for any speed difference which may occur between the primary and secondary axles. When the secondary axle is a front axle, an open differential is typically installed. Torque-sensing differentials with clutch pack pre-load are not considered acceptable for front axles due to steering issues attributable to torque bias. The front wheels tend to slide rather than turn on low coefficient-of-friction surfaces.
The present invention comprises a radial-type clutch that supplies on-demand power to, for example, the front wheels of a vehicle, while allowing the front wheels to overspeed the rear wheels. The clutch comprises a driving member having a plurality of radially-outwardly-biased pawls, a reversing ring, a driven member having a plurality of notches, and a housing having a plurality of pawls. The pawls on the driving member engage outwardly concentric notches on the driven member, and are activated and deactivated by inner reversing cams of the reversing ring. The pawls in the housing engage notches in the outer surface of the reversing ring, which causes the reversing ring to move between a first position and second position relative to the driving member. The engagement of the housing pawls with the reversing ring notches is regulated by the driving member.